ClearDarkSky

Based on a numerical weather model, Clear Sky Charts are
perhaps the most accurate and the most usable forecasters of astronomical
observing conditions for over 1900 observatories and observing sites in
North America.

A web database which allows observers all over North America to enter observations
of seeing (atmospheric turbulence which causes loss of telescopic resolution)
and correlates them to seeing forecasts. The data is used to refine numerical
forecast models.

The web pages, computer programs and databases at cleardarksky.com are written
by: